怎样判断一个英语句子是什么时态?

纯动词原形就是现在时态 I love my girl friend !
V+ed/动词过去式 是一般过去时态 I loved you !
will+V原形/be going to 是一般将来时
I will go to school.
have/has+done（动词过去分词）现在完成时
I have finished my homework.
She has finished her homework.
had+done（动词过去分词）过去完成时
I had finished my homework.
那你就要看语境啦!看时间状语啦!只有这样啦!你慢慢体会吧!祝你早日找到方法!

看前后文

一般句子中又表示时间的单词,表过去的比如last night,this morning,yesterday等,一般现在时的就是动词用原型之类的,将来时则will,be going to do,in the future等,其他完成时态,一般现在时:I make love with her everyday.
一般过去时:I made love with her yesterday.

看前后文,不好解释,得长篇大论半天才可以,主要是一个积累,楼上已经回答的不错了,我补充补充.

看动词是现在式，还是过去式，比如说do ,did/work,worked
看时间提示：yesterday,tomorrow
将来式是 will,be going to等句式后